BIO444 Exam2 Study Guide

T-cell receptor (TCR)

Recognizes peptide fragments presented in the MHC.

B-cell receptor (BCR)

Antibody bound to the surface of B cells.

Major histocompatibility complex (MHC)

Also known as human leukocyte antigens (HLAs), involved in antigen presentation.

HLA alleles

Most people have 12 different HLA alleles; over 14,000 known in the human population.

Antigen presenting cell (APC)

Any cell with MHC on its surface.

MHC class I

Found on all nucleated cells; presents peptides 8 to 10 amino acids long recognized by CD8+ T cells.

MHC class II

Found only on professional APCs; presents peptides 10 to 30 amino acids long recognized by CD4+ T cells.

CD8+ T cells

Also known as cytotoxic T cells (CTLs), recognize MHC class I.

CD4+ T cells

Also known as helper T cells, recognize MHC class II.

T Cell Receptors (TCRs)

Made of immunoglobulin domains, usually composed of α and β subunits.

γδ T cells

TCRs occasionally made of γ and δ subunits, poorly understood.

Somatic recombination

Process by which TCRs are formed from VDJ gene segments.

T cell maturation

Occurs in the thymus over 1-3 weeks, starting as double negative (DN) progenitor T cells.

Positive selection

Pre-TCR must recognize MHC class I or II to survive.

Double positive T cells

T cells that express both CD4 and CD8 after completing TCR formation.

Single positive T cells

T cells that lose either CD4 or CD8 based on MHC recognition.

Negative selection

Removal of strongly self-reactive T cells to prevent autoimmune responses.

AIRE (autoimmune regulator)

Transcription factor driving expression of tissue-specific antigens in mTECs.

Naïve T cells

Surviving T cells that leave the thymus and travel to secondary lymphoid organs.

T cell activation

Requires three signals:antigen presentation, costimulatory signals, and polarizing cytokines.

IL-2

A potent T cell growth factor secreted upon activation, promoting T cell proliferation.

Cytotoxic T Cells (CTLs)

Produce cytotoxins like perforin and granzymes to induce apoptosis in target cells.

T Helper Cells (TH cells)

Produce cytokines that direct and coordinate the immune response.

TH1 cells

Stimulate phagocyte-mediated killing of infected cells; signature cytokine is IFN-γ.

TH2 cells

Activate responses to multicellular organisms; signature cytokines are IL-4, IL-5, and IL-13.

TH17 cells

Activate responses to extracellular bacterial and fungal infections; signature cytokine is IL-17.

Follicular helper cells (TFH)

Activate B cells and enhance antigen presentation efficiency.

Regulatory T cells (Treg)

Limit activities of effector T cells and secrete immunosuppressive cytokines.

Memory T Cells

Long-lived T cells that maintain a pool ready to respond rapidly to returning pathogens.